The invention is based on a method as defined hereinafter. In one such method, known from European Patent Disclosure EP A 1 114 991, the fuel is injected into the applicable combustion chamber of the cylinders of the associated engine in such a way, with the aid of a specially designed fuel injection pump, that in the lower load range of the engine, that is, at partial load, the injection into the engine combustion chamber takes place just before top dead center or immediately before ignition of the fuel-air mixture. Conversely, at full load, in this known injection method the injection takes place in the course of the intake stroke of the engine piston that defines the combustion chamber, in the range between its top dead center and its bottom dead center. Ignition of the fuel-air mixture forming in the combustion chamber is effected by means of a spark plug, and the air delivered to the combustion chamber is supplied unthrottled, or in other words without throttling of the aspirated air by a throttle valve as is otherwise usual in engines with externally supplied ignition. By the known method, the intent is to enable substantially improved filling of the combustion chambers, along with a reduction in fuel consumption, and load regulation is done by controlling the injection quantity. With respect to preparation of the fuel to be injected, the circumstance is taken into account that with a large fuel injection quantity, corresponding to full-load operation, an approximately stoichiometric fuel-air mixture can be established, and the fuel is therefore already introduced at the proper time in the intake stroke of the engine, so that by the time of its ignition it can mix well with the air that is present. At small injection quantities, however, in accordance with the unthrottled delivery of air to the combustion chamber, a substantially larger proportion of air is present in comparison with the fuel introduced, so that an ignitable mixture is nevertheless achieved by later injection, particularly into the vicinity of the spark plug,
With a view to the desired reduction in fuel consumption with a simultaneous lowering of all the polluting components of the exhaust gas, however, the known method has the disadvantage that in the partial load range, very high air-fuel ratios of lambda=5 and higher occur; in lean operation as well, crude NOx emissions are high, which because of the air excess cannot be catalytically treated afterward, so that the nitrogen oxide emissions are higher than called for by regulations. Nevertheless, for engines that work with aspirated air throttling and with regulation of the exhaust gas and air composition to lambda=1, the known method has the advantage of substantially better fuel consumption, especially in the partial-load range.